1. Field of the Invention
The present invention relates to mounting an integrated circuit to a substrate, and in particular to connection between IC leads in an integrated circuit package and lands for mounting on a substrate.
2. Description of the Related Art
An integrated circuit package of a type which is mounted on the surface of a substrate is provided with a plurality of IC leads each being a part to be connected with the substrate. These IC leads are electrically connected reliably with a plurality of lands for mounting on the substrate by the use of a melting conductive material such as solder, in general. FIG. 1 shows solder 92-n (n: an integer) supplied on lands 32-n (n: an integer), and corresponding IC leads 12-n (n: an integer) in an integrated circuit package 10. A connecting process therefor is carried out as described hereinafter. Each solder 92-n (n: an integer) is supplied on each land 32-n (n: an integer) in accordance with a predetermined printing manner, and then each IC lead 12-n (n: an integer) is located to be rested thereat. Thereafter, the solder is melted by means of, for example, reflow soldering, whereby each IC lead 12-n is electrically connected to each land 32-n (n: an integer). When the integrated circuit package 10 is connected to the substrate 30, the integrated circuit package 10 can send and receive signals to and from other components of the substrate 30 through each leader line wiring 34-n (n: an integer).
There is a case where IC lead in the integrated circuit package 10 is deformed in handling the same in a preceding stage such as a manufacturing stage for mounting the integrated circuit package 10. Particularly, it is known that an end IC lead 12-1 positioned at the end of the integrated circuit package 10 is easily deformed. FIG. 1 shows the end IC lead 12-1 which has been deformed. The term xe2x80x9cdeformationxe2x80x9d means herein a case where, for instance, a part of the IC lead is bent upwards, so that there is no predetermined twodimensional contact with respect to a substrate.
Heretofore, since an amount of each solder 92-n (n: an integer) to be supplied to each land 32-n (n: an integer) is equal, complete soldering could not have been performed between the end IC lead 12-1 and an land 32-1. FIG. 2 shows a state where the end IC lead 12-1 is connected to the land 32-1 by means of solder 92-1 wherein since the end IC lead 12-1 has been deformed upwards, either the end IC lead 12-1 is not i n contact with the solder 92-1 or only a part thereof is in contact with the solder 92-1. In this respect, FIG. 2 shows a state where the end IC lead 12-1 is in contact with the solder 92-1 in only a region A. The minuter region A brings about the higher possibility of disconnection due to some oscillation or the like. Under the circumstances, it is not concluded that soldering has been completed sufficiently. If the end IC lead 12-1 has not been essentially in contact with the solder 92-1, a purpose for soldering is never achieved. Such a resultant substrate is determined as a defective good as a result of inspection. Thus, for example as a rework, further solder is supplied manually onto the end IC lead 12-1, and then it has to be melted.
In this connection, for example, Japanese Patent Laid-Open No. 169153/1994 discloses such a technology that a more amount of solder is to be supplied to an end pad. However, this technology is the one to be applied for an end pad having a wider area than that of a usual end pad. Accordingly, when an end pad contains a wide area, a movable range of solder expands, so that a deformed end IC lead cannot be connected in a sufficiently firm condition after all.
An object of the present invention is to provide a method for connecting reliably a deformed IC lead to a land.
Another object of the present invention is to provide a substrate for mounting an integrated circuit package connected by means of the method as described above.
According to the present invention, a method for mounting an integrated circuit package on a substrate, wherein the integrated circuit package includes a first lead being nondeformed and connected to a first land for mounting on the substrate, a second lead being deformed and connected to a second land for mounting on the substrate, comprises a step of supplying conductive material on a land on the substrate wherein an amount of the conductive material larger than that of the first land is supplied to the second land; and melting the conductive material supplied to connect a leald in the integrated circuit package with the land wherein the conductive material molten on the first land extends in the vertical direction with respect to the substrate with a first height thereby connecting the first lead with the first land, while the conductive material molten on the second land extends with a second height higher than the first height due to surface tension thereby connecting the second lead with the second land. As a result, one of the above described objects of the present invention is achieved.
Preferably, the integrated circuit package includes a plurality of leads and the second lead is an end lead positioned at the end of the plurality of leads.
For example, the step for supplying the conductive material onto the second land is a step for supplying a much larger amount of the conductive material onto the second land at a position opposed to the first land.
According to the present invention, a substrate for mounting an integrated circuit package comprises an integrated circuit package provided with a first lead and a deformed second lead, the first lead being nondeformed and the second lead being deformed; the substrate provided with a first land and a second land; a conductive material on the first land, which has a first height in the vertical direction with respect to the substrate and which connects the first lead with the first land; an amount of the conductive material on the second land larger than that of the conductive material on the first land, which has a second height higher than the first height due to surface tension produced in the case where the conductive material is melted and which connects the second lead with the second land. As a result, the other of the above described objects of the present invention is achieved.
Preferably, the integrated circuit package includes a plurality of leads and the second lead is an end lead positioned at the end of the plurality of leads.